The present invention relates to valves of the type employed for controlling purging of fuel vapor stored in a canister connected to receive vapors from a vehicle fuel tank and for introducing the vapor purge flow into the inlet of the vehicle engine. Such valves are known in the art and typically utilize a vacuum signal such as from the engine manifold, to control the pressure on one side of a power diaphragm employed to control the movement of a valving member or obturator with respect to a valve seat or port for controlling flow of the vapor between the canister and the engine inlet. In order to provide electrical control of the vapor purge flow to the engine inlet where the engine operation is controlled by electrically actuated fuel injectors an electrically operated valve is employed to control atmospheric bleed to a vacuum signal chamber on one side of the power diaphragm.
However, vapor management valves of the aforesaid type employing a vacuum generated control signal for the power diaphragm are effected by changes in the engine manifold vacuum. When the engine throttle is closed, from an engine loaded condition, a strong manifold vacuum is applied through the regulator valve outlet to the underside of the power diaphragm. The restrictor in the vacuum signal port causes a lag in the corresponding vacuum level being created above the power diaphragm in the vacuum signal chamber; and, therefore the diaphragm is moved downwardly by the pressure differential to substantially decrease the vapor purge flow to the engine inlet. This condition is sometimes referred to as "tip-out" and can result in an overly lean fuel/air mixture and can cause engine stalling, particularly at engine idle.
It has thus long been desired to provide a way or means of providing for improved control of fuel vapor canister purge in a vehicle engine emission control system and to provide such improved control a relatively low cost and an easy to manufacture valve and to provide for electrical control of the purge valve in a manner which can accommodate or compensate for changes in engine manifold vacuum as experienced when the throttle is closed during engine operation.